Bearded Iris are identified by thick, bushy “beards” on each of the falls (lower petals) of the blossoms. Originally, most of these were native to central and southern Europe. The American Iris Society has divided the bearded irises into six groups for garden judging awards.
Miniature Dwarf Bearded (MDB) — the tiniest of bearded irises, with height of up to 20 cm (8 inches). They are also the earliest to bloom. They are most effective in rock gardens or planted in drifts where they make a “carpet of color.”
Standard Dwarf Bearded (SDB) — some of the most useful garden plants, ranging in height from 20 cm (8 inches) to 41 cm (16 inches). They begin their bloom as the MDBs are ending, still quite early in the iris season. They are best displayed in clumps where they give the effect of a “cushion” of individual blooms. The colors are nearly unlimited since the SDBs show all the different “spot patterns” of the miniatures, as well as the plicatas and pinks seen in the TBs.
Intermediate Bearded (IB) — stand from 41 cm (16 inches) to 70 cm (27 1/2 inches) high, with their bloom season overlapping the SBDs and the TBs. Although the IBs show their dwarf ancestry in early bloom season and very interesting color patterns, they are large enough that their individual stalks may be nicely branched, forming an elegant bouquet. Some varieties are nicest in clumps, where they present a large amount of color (like the SDBs), while others are showiest in specimen plantings, where the stalks and individual blooms may be seen to best advantage.
Border Bearded (BB) — essentially small versions of the TBs in the same height range and bloom size as the intermediates, but blooming with the tall beardeds. Good BBs have round, ruffled petals that complement their small size.
Miniature Tall Bearded (MTB) — this class is distinguished by daintiness and delicacy. Height from 41 cm (16 inches) to 70 cm (27 1/2 inches). The blooms are smaller than on a BB and the stems are thin and wiry. An MTB clump looks like a cloud of butterflies. They are often called “Table Irises” because they are so well suited for arrangements.
Tall Bearded (TB) — have stalks with a height of 70 cm (27 1/2 inches) and above, with branching and many buds. Each stalk, in itself, makes a stately arrangement in the garden or in a vase. In addition to a wide variety of colors and patterns, the TBs display other qualities (such as ruffling and lacing) more frequently than do the other classes
Even if you grow nothing but bearded irises, you can enjoy a remarkable range of color and a bloom season extending for months. Some bearded irises are “rebloomers”, blooming again in the summer, fall or winter. Additional water and fertilizer applied during the summer months encourages them to bloom again. There are now reliable attractive rebloomers available which will perform in all but the coldest climates.
Incidentally, the word “median” refers to all the bearded irises except the miniature dwarfs and the tall beardeds; that is to say the SDBs, IBs, BBs and the MTBs. Strictly speaking, the word “dwarf” means only the MDBs.